This invention relates to gas turbines, and more particularly, to a liquid fuel nozzle having a passive protective purge for protecting the nozzle from damage when neither liquid fuel nor active purge is flowing through the nozzle.
Industrial gas turbines often are capable of alternatively running on liquid and gaseous fuels. These gas turbines have fuel supply systems for both liquid and gas fuels, e.g., natural gas. The gas turbines generally do not simultaneously burn both gas and liquid fuels. Rather, when the gas turbine burns liquid fuel, the gas fuel supply is turned off and vice-versa. The fuel system that is not being used is usually purged with air.
Gas turbines that burn liquid fuels require a liquid fuel purge system to clear combustor fuel nozzles of liquid fuel. Air is typically used to actively purge unused combustor nozzle passages during turbine operation. Purge air supplied from an external source is regulated by a control valve. When the fuel system is activated or deactivated during turbine operation, the purge air needs to be turned on or off. The purge air and fuel are generally not permitted to be xe2x80x9conxe2x80x9d at the same time for safety reasons. Thus, when activating a fuel system, the purge air is shut xe2x80x9coffxe2x80x9d before the fuel is turned on, and when deactivating a fuel system, the fuel is shut xe2x80x9coffxe2x80x9d before the purge air is turned xe2x80x9conxe2x80x9d. This sequence results in a brief period during which there is neither fuel flow nor purge air, thus opening the possibility of ingesting combustion gases into the fuel nozzle. The brief no-flow period may also cause thermal distress of the fuel nozzle.
In one existing approach, the time-period during which both the fuel and-purge air are xe2x80x9coffxe2x80x9d is minimized for preventing fuel nozzle damage during a brief no-flow period. There are practical limits, however, as to how short this time-period can be set. Also, flowing purge air quickly to a fuel system that is full of fuel due to a prior operation may force the left over fuel into the combustor and produce an undesirable surge in turbine output. Further, the turbine control system requires some minimum time to confirm that a fuel valve or a purge air valve is in fact closed before opening the control valve to the other.
In another existing approach, a portion of combustor inlet air is diverted to wash over an outer exit of a fuel nozzle passage so that any back-flow into the nozzle will be just air and not hot combustion products. This approach, however, is not only difficult to implement but also includes performance side effects.
Therefore, there is a need for a system and method to overcome the above-identified drawbacks.
Accordingly, a solution to overcome the problems identified in the prior approaches is proposed. Specifically, a liquid fuel nozzle having a passive protective purge in order to protect the nozzle from damage during periods when neither liquid fuel nor active purge is flowing through the nozzle is shown.
In accordance with one embodiment of the present invention, there is provided an apparatus and method for purging a liquid fuel nozzle and protecting the same from back-flowing combustion gases during a transition period when neither liquid fuel nor active purge are flowing through the nozzle. Specifically, the apparatus includes a liquid fuel nozzle having a first passageway for carrying fuel (xe2x80x9cfuel passagewayxe2x80x9d), a second passageway disposed adjacent to the fuel passageway for carrying purge air. The second passageway is further capable of carrying water into a combustor. A third passageway is provided for carrying atomizing air into the combustor. A crossover passage or a conduit interconnects the fuel passageway to the second passageway in order to divert high-pressure air from the second passageway into the fuel passageway, thus preventing ingestion of backflowing combustion gases.
During a period when operation of the gas turbine is shifted from gas fuel to liquid fuel or viceversa, when both the liquid fuel and liquid fuel purge air are shut off from flowing into the combustor via the fuel passageway, purge air flowing through the second passageway continues to flow. A portion of the purge air is diverted into the fuel passageway via the crossover conduit to prevent ingestion of combustion gases into the nozzle, thus protecting fuel nozzle tips from deteriorating.
In another embodiment, the liquid fuel nozzle includes a plurality of passageways, one of the passageways being a fuel passageway. A crossover conduit interconnects the fuel passageway to a select one of the plurality of passageways to enable fluid flow therebetween. High-pressure air from the select passageway is diverted into the fuel passageway via the conduit to purge the liquid fuel nozzle.
In its broader aspects a gas turbine having a compressor, a combustor and a turbine, a gaseous fuel supply coupled to provide gaseous fuel to the combustor, and a liquid fuel supply coupled to provide liquid fuel to the combustor via a nozzle assembly is provided. The nozzle assembly includes a plurality of passageways for flowing a fluid into the combustor, one of the passageways being a fuel passageway, a conduit interconnecting the fuel passageway to one of the plurality of passageways to enable fluid flow therebetween. One of the plurality of passageways flows high pressure air. High pressure air from one of the plurality of passageways is diverted into the fuel passageway via the conduit to protect the nozzle from ingestion of hot combustor gases. The plurality of passageways flow air when the gas turbine is operating on gas fuel. One of the passageways is an atomizing air passageway which flows air at a higher flow rate when the gas turbine is operating on liquid fuel. The first end of the conduit is coupled to the fuel passageway and an opposite second end is coupled to one of the plurality of passageways. The first end of the conduit is preferably coupled to the fuel passageway at a location downstream of a first swirler arranged in the fuel passageway. The second end of the conduit is preferably coupled to one of the plurality of passageways at a location upstream of a second swirler arranged in the one of the plurality of passageways.
In another aspect, a liquid fuel nozzle assembly for supplying liquid fuel to a combustor of a gas turbine, the nozzle assembly comprising a fuel passageway for flowing liquid fuel into the combustor, a second passageway disposed adjacent to the fuel passageway for flowing purge air into the combustor, the fuel and second passageways interconnected via a conduit to enable fluid flow therebetween to protect the nozzle from ingestion of hot combustor gases. The nozzle assembly further comprises an atomizing air passageway for flowing atomizing air into the combustor, the atomizing air passageway flows air at a higher flow rate when the gas turbine is operating on liquid fuel.
In yet another aspect, a dual fuel gas turbine having a compressor, a combustor and a turbine, a method of purging a liquid fuel nozzle comprising the steps of flowing fluids into the combustor via a plurality of passageways of the nozzle, one of the passageways being a fuel passageway. The fuel passageway is coupled to one of the plurality of passageways via a conduit. One of the plurality of passageways flows high pressure air. High pressure air from one of the plurality of passageways is diverted into the fuel passageway to protect the liquid fuel nozzle from ingestion of hot combustor gases.
In a further aspect, a method of protecting a liquid fuel nozzle used in a dual-fuel gas turbine having a compressor, a combustor, and a turbine, the method comprising flowing liquid fuel via a fuel passageway into the combustor, flowing purge air into the combustor via a second passageway disposed adjacent to the fuel passageway and interconnecting the fuel and second passageways via a conduit to enable fluid flow therebetween to protect the nozzle from ingestion of hot combustor gases.
In another aspect, a method for purging a dual fuel gas turbine having a combustor, a compressor and a turbine, the method comprising the steps of supplying liquid fuel to the combustor via a nozzle having a plurality of passageways, one of the passageways being a fuel passageway, interconnecting the fuel passageway to one of the plurality of passageways via a conduit to enable fluid flow therebetween, and protecting the nozzle from ingesting backflow combustion gases by diverting high pressure air from one of the plurality of passageways into the fuel passageway via the conduit.
In yet another aspect, a gas turbine having a combustor, a compressor and a turbine, a nozzle for supplying liquid fuel to the combustor, a method of passively purging liquid fuel from the nozzle comprising flowing liquid fuel into the combustor via a fuel passageway, flowing high pressure air into the combustor via a second passageway disposed adjacent to the fuel passageway. The fuel and second passageways are interconnected via a conduit to enable flow of high pressure air from the second passageway into the fuel passageway to prevent ingestion of backflow combustion gases into the nozzle.
In another aspect provides a dual-fuel gas turbine having a compressor, a combustor, and a turbine, a method of protecting a liquid fuel nozzle from ingestion of backflow combustion gases. The method includes flowing liquid fuel into the combustor via a fuel passageway, flowing high pressure air into the combustor via a second passageway, and interconnecting the fuel and second passageways via a conduit to direct flow of high pressure air, from the second passageway to the fuel passageway, into the combustor.